Department of Neurological Sciences, University of Verona, Verona, Italy.
PLoS One. 2013;8(2):e56144. doi: 10.1371/journal.pone.0056144. Epub 2013 Feb 7.
Transgenic mice expressing fluorescent proteins in specific cell populations are widely used for in vivo brain studies with two-photon fluorescence (TPF) microscopy. Mice of the thy1GFP-M line have been engineered for selective expression of green fluorescent protein (GFP) in neuronal populations. Here, we report that TPF microscopy reveals, at the brain surface of these mice, also motile non-neuronal GFP+ cells. We have analyzed the behavior of these cells in vivo and characterized in brain sections their immunophenotype.With TPF imaging, motile GFP+ cells were found in the meninges, subarachnoid space and upper cortical layers. The striking feature of these cells was their ability to move across the brain parenchyma, exhibiting evident shape changes during their scanning-like motion. In brain sections, GFP+ cells were immunonegative to antigens recognizing motile cells such as migratory neuroblasts, neuronal and glial precursors, mast cells, and fibroblasts. GFP+ non-neuronal cells exhibited instead the characteristic features and immunophenotype (CD11c and major histocompatibility complex molecule class II immunopositivity) of dendritic cells (DCs), and were immunonegative to the microglial marker Iba-1. GFP+ cells were also identified in lymph nodes and blood of thy1GFP-M mice, supporting their identity as DCs. Thus, TPF microscopy has here allowed the visualization for the first time of the motile behavior of brain DCs in situ. The results indicate that the thy1GFP-M mouse line provides a novel animal model for the study of subsets of these professional antigen-presenting cells in the brain. Information on brain DCs is still very limited and imaging in thy1GFP-M mice has a great potential for analyses of DC-neuron interaction in normal and pathological conditions.
转基因小鼠在特定细胞群体中表达荧光蛋白，广泛用于双光子荧光（TPF）显微镜的活体脑研究。thy1GFP-M 系的小鼠经过工程改造，可在神经元群体中选择性表达绿色荧光蛋白（GFP）。在这里，我们报告 TPF 显微镜在这些小鼠的脑表面还揭示了运动的非神经元 GFP+细胞。我们分析了这些细胞的体内行为，并在脑切片中对其免疫表型进行了特征描述。通过 TPF 成像，在脑膜、蛛网膜下腔和上皮质层发现了运动的 GFP+细胞。这些细胞的显著特征是它们能够在脑实质中移动，在扫描样运动过程中表现出明显的形状变化。在脑切片中， GFP+细胞对识别运动细胞的抗原（如迁移性神经前体细胞、神经元和神经胶质前体细胞、肥大细胞和成纤维细胞）呈免疫阴性。GFP+非神经元细胞表现出树突状细胞（DCs）的特征和免疫表型（CD11c 和主要组织相容性复合体分子 II 免疫阳性），并且对小胶质细胞标志物 Iba-1 呈免疫阴性。在 thy1GFP-M 小鼠的淋巴结和血液中也鉴定出 GFP+细胞，支持它们作为 DCs 的身份。因此，TPF 显微镜首次允许在原位可视化脑 DCs 的运动行为。结果表明，thy1GFP-M 小鼠系为研究大脑中这些专业抗原呈递细胞的亚群提供了一种新的动物模型。关于脑 DCs 的信息仍然非常有限，在 thy1GFP-M 小鼠中的成像具有分析正常和病理条件下 DC-神经元相互作用的巨大潜力。
